Tandem axle suspension systems conventionally have tandem axle assemblies with ends of the axle assemblies interconnected via springs and torque rods to support brackets which are connected to frame members of a vehicle. Usually, the springs are connected to a heavy trunion or shaft which extends across the vehicle between two frame support brackets on opposite sides of the vehicle. The support brackets are connected to the axle assemblies by spring and stabilizing devices, notably torque rods having proximal ends connected to the brackets and distal ends connected to the axle assemblies.
Conventionally the brackets are constructed in two parts. A main upper portion of each bracket is connected to the frame. A lower bracket is connected to a lower end of a main bracket and a portion of the lower bracket extends out and upward for securing a proximal end of a lower torque rod.
An example of such construction is shown in U.S. Pat. No. 2,810,587.
When vehicles are rolling at constant speed, the torque rods have stresses caused by differences in surfaces upon which the vehicle is moving and vehicle reactions. Stresses on the torque rods are increased upon changes in vehicle speeds, accelerations and decelerations, and are notably increased upon braking. During acceleration and deceleration forces are transferred in the longitudinal direction of the vehicle between the axle assemblies and the frames via the torque rods and support brackets. Longitudinal forces transferred by the lower torque rods, especially the increased forces transferred during rapid braking, are concentrated in the interconnection between the lower bracket and the main bracket.
Conventionally, the shear stresses which have tended to separate the two brackets have been withstood by plural bolts, as an example eight or more bolts which connect each lower bracket to the main bracket. A result has been that repeated shear stresses under severe braking conditions may weaken or fracture or sever one or more bolts. The problem persists and heretofore has not been satisfactorily solved.